Borosilicate
(hard glass) is a boron based glass and is called
hard because it has a higher melting temperature, does not hold
heat very long, has a short working time when removed from the
flame and is stiffer than soft glass. Glass Alchemy, Northstar,
Colormax, Momka, Duran and Pyrex are all hard glasses.What is Borosilicate Glass?
Borosilicate glass is a very unique and specialized variety of glass.
Its composition is different from the "soft" glass that
is normally used for beads, paperweights, art glass bowls, ornaments,
etc. Borosilicate glass is far stronger than "soft" glass and
has been used for everything from stovetop cookware to nuclear waste
containment. One of its most frequent uses is to make scientific
glassware such as beakers and test tubes.

Chemical Composition Chemically speaking, borosilicate glass substitutes boron
oxide particles in place of the soda and lime particles found in
soft glass. The boron oxide serves as a flux or glue to hold the
silicate particles together with aluminum oxide and sodium oxide.
Because the boron oxide particles are so small, the silicate is held
together more closely resulting in a much stronger glass. Borosilicate
glass is also highly resistant to the strongest of chemicals and
acid compounds.

Unusual Durability! One big reason we prefer to work with borosilicate glass
is because it results in a much stronger finished piece. It will
stand up to a lot of wear and tear without having to treat it as
carefully as soft glass jewelry. It often amazes people how many "accidents" this
glass can survive without breaking or cracking. Unlike soft glass,
Borosilicate glass is also immune to the corrosive (etching) effects
of natural fatty acids found on human skin and the Alphahydroxy acids
found in many skin care lotions and treatments currently on the market.

Unique Color Palette Another major reason for using borosilicate glass is the
amazing color palette available. There are actually fewer colors
available to work with but each one is an organic, living color that
can be manipulated and shaded with careful torch work and annealing.
The finished piece appears much more dynamic and vibrant. Also, because
of the chemical composition of borosilicate glass, different precious
metals such as silver and gold may be used to color the glass in
some very unique and amazing ways.

"Dichroic Glass" is somewhat of a misnomer, since the dielectric
coating that produces all the interesting colors is not glass at all, but
a group of very thin layers of metal oxides. This stack of thin layers
has a total thickness of three to five millionths of an inch. The layers
produce an "interference filter", creating the varied and unique
color characteristics we see. Since the filter is so thin, it has very
little mechanical integrity of its own, and must be supported on a mechanically
stable substrate. Glass is the ideal candidate for this substrate. Transparent,
rigid and stable, it withstands high temperatures, and is not affected
by moisture, solvents or most acids. The filter materials are actually
more chemically stable than most glasses used as the substrate. Thus, what
we commonly call "Dichroic Glass", is actually a piece of dielectric
interference filter attached to the surface of a piece of glass.

Dichroic is defined as the property of having more than one color, especially
when viewed from different angles. Dichroic glass is a high-tech spin-off
of the space industry. Thin layers of metallic oxides, such as titanium,
silicon, and magnesium are deposited upon the surface of the glass in a
high temperature, vacuum furnace.

The glass to be coated is carefully cleaned, and fastened to a planetary
arm in the top of the furnace chamber. The oxides are placed in a crucible
on the bottom of the chamber. Air inside of the chamber is removed with
a high vacuum-producing cyropump, and the chamber is heated to 300oF. The
metallic oxides are vaporized by an electron beam, and the rotating glass
target is evenly coated with many thin layers. The resulting color is determined
by the individual oxide compositions.

Dichroic coatings transmit certain wavelengths of light, while reflecting
others, thus creating an interference-effect similar to the iridescence
observed in Nature's fire opal, dragonfly wings and hummingbird feathers.
The transmitted color is different than the reflected color, and a third
color is produced by viewing the dichroic piece at a 45o angle. The resulting
colors are pure, saturated, single wavelengths of light, that appear to
originate from within the dichroic piece.